A warm human fantasy about a little planet near the Earth -- this is a young science fiction yarn. The story opens with a mysterious advertisement for a space ship to be built by two boys who want to do a good deed. The commission comes from a kindly little spore man, Dr. Tyco Bass, whose people back on his planet, Basidium, are in a plight. The plants from which they get their essential sulphur are dying. The two boys who answer the ad are David and Chuck, of Pacific Grove, California. On their mission, they take a hen for the Basidium-ites to raise, for the sulphur from its eggs. As a by-product of the visit, the boys inspire the mushroom people with the spirit of modern science, to offset their impractical dreaming. Sounds a bit mad- but it's tops for reading. And young S-F is hard to come by.